which gives extremely few spores or none at all, are, in this respect, easy to control. If, on the other hand, a brewery yeast with strong spore formation has to be dealt with, the matter is somewhat more difficult. From the above it remains that we are able to take from the cells their power of forming spores, thereby making the analysis easier. Hansen has done this several years ago for Carlsberg bottom yeast No. 2, and has brewed good normal beer with the new variety formed in this manner. Yet it must be kept in mind that the transformed species may also undergo a simultaneous change in other respects. The sporeless variety will often act in a brewery in a different manner to its parent form. The experiments carried out with Carlsberg bottom yeast No. 1 are additional examples of the practical application of the results of the researches on variation. This yeast gives a beer that is stable, but greatly attenuated during the primary fermentation. Now Hansen has, by the method of culture described, prepared from it at a high temperature a permanent variety with less attenuating power which gives a fuller beer than the parent form. This variety has, however, one failing; it acts too slowly.

Numerous articles on the variation of beer yeast are to be found in the brewery journals both before and after the introduction of the pure culture system; the most of these treat of their degeneration in practice, others of their improvement. The attainment of the latter was sought in one way by their cultivation in any culture liquid of definite chemical composition. The best known researches in this direction are those made by Hayduck. According to him the enrichment of the yeast with nitrogen is one of the causes of degeneration; in such cases, in order to regenerate the yeast, he recommends that it should first, before pitching, be allowed to ferment in a cane sugar solution. Seyffert found recently that a yeast which had hitherto given a

good clarification in the brewery, but which suddenly went bad in that respect, could be brought round again to give a good clarification by the addition of gypsum to the brewing water. The experiments with stimulating antiseptics already mentioned made by Biernacki, Effront, Hayduck, Heinzelmann and Schulz come under this head. Besides Hansen, Delbrück, Jörgensen, Kukla and Will have published papers on the variation of brewery yeast. Hansen's two new varieties of beer yeast and his experiments with them in practice have been described. These experiments assume a special interest from the fact that the two species which formed the starting points for the transformation are well known, and are present in most laboratories, and also from the fact that a definite method is given. This does not hold for the experiments described below which start with the object of attaining a racial improvement by selection in seeding.

The application of the pure culture system in practice consists, as we have seen, not only in the preparation of pure cultures of a certain species or race, but at the same time in a selection from among the vegetations produced by the individuals. Thus with the introduction of the pure culture system into the brewery a racial improvement is at the same time striven after. It was a case here of always selecting the best, since practical men always made greater demands and forced us to experiment, i.e., compelled us to seek for such individuals as satisfied these demands. It is not only required that the species or race shall keep all those properties which are of value for the practical man, but it is desired that at the same time such individuals shall be selected as will vary in a manner serviceable to the brewery concerned, i.e., possess good qualities in a high degree and lose undesirable ones. Of course even in the best cases this may be only partially attained. The yeast

species selected by Hansen for the two Carlsberg breweries was the one which became known as Carlsberg bottom yeast No. 1, which has its good qualities (good taste, great stability), but also its less desirable ones (sluggish clarification, somewhat too great attenuation). He then began at once to improve the race by continual selection, and his successors have, later on, worked in the same direction, outside the Carlsberg laboratory as well, not only with this species but with other species and races.

Racial improvement thus consists in repeated selection of the best individuals. It may be seen from the papers published by Hansen and other investigators on experiments in this direction that it is not possible to set up definite rules here. Experiments must be carried out. The experimenter will often be deceived and arrive at an undesirable result; he is here confronted by something which is not to be regulated. It is a matter quite different from the mere preparation of the above asporogenous races; in the latter case the conditions are known exactly and the transformation can be regulated. Finally it must be borne in mind that, even when the material for such experiments on racial improvement is taken from the contents of the brewery fermenting vats, there is no guarantee that the race taken out stands in genetic connection with that formerly selected. They are not therefore of necessity blood relations because both agree in botanical characteristics.

Similar communications on racial improvement have been made by the technologists of wine fermentation, but here also there is no mention made of definite methods. In all these communications also, information about the species from which the start was made is as a rule wanting.

A culture yeast may also be subject in practice to

In

variation in a harmful direction. Hansen in his Practical Studies in Fermentation, when in 1892 summing up his experiments on this subject during the course of years, says as follows: "When we regard the variations of yeast in brewery practice from a biological point of view, we are inclined to look upon them as quite insignificant; for the practical brewer, however, the matter is quite different. The changes can, indeed, occur in a very disagreeable manner, and sometimes cause an appreciable irregularity. In the course of a year they pass like a wave through the brewery, and in most cases we have no idea of their cause." Investigations on all that occurs in practice are difficult in a high degree, not only because we do not work here with the absolutely pure culture of the culture yeast concerned, but the composition of the wort and other external factors are so very complicated and variable that they frequently escape our control. spite of very extended and arduous attempts on the part of the author by experimental means to shed light on the most important questions which have cropped up in this region of late years, he is still unable to record completely satisfactory results, but hopes later to be able to give some elucidations. This may, however, be said, that those variations which come to light in actual practice under the influence of the factors there predominant are only transient, which shows that the pure culture system has not only gained a firm foothold in the brewing system of the whole world, but daily spreads further into all the other alcohol fermentation industries. Some of the culture yeasts are particularly permanent, whilst others are more inclined to variation. Carlsberg bottom yeast No. 1 belongs to the first of these. In the New Carlsberg Brewery, for instance, there was a pure culture of this species in the fermentation cylinder of the pure culture apparatus which

had been introduced more than five years before. Fluctuations of course occurred, but no fixed changes. Various authors have made communications on a special constancy in culture yeasts. The experiments on this point by Irmisch, Jörgensen and P. Lindner are noteworthy. Finally, if in practice a yeast growth is present which exhibits a variation in an adverse direction, a degeneration, the means of cure are now easily accessible; a new culture is then introduced.

10.-Circulation in Nature.

We will now shortly describe what is so far known of the circulation of the saccharomycetes in nature.

In the years 1880-81 Hansen published the results of one of the most important and most interesting biological researches on yeast cells which we possess, and which he had carried out in the preceding years with the cells of the yeast named Saccharomyces apiculatus, Reess. From it we find that this fungus occurs and fructifies in summer and autumn on the injured parts of sweet juicy fruits, in the juice of which it multiplies; during winter and spring it is found in the ground under the fruit and only in quite exceptional cases in other places. It gets into the ground partly through the falling of the fruit and partly by means of the rain which trickles over the fruit. Those cells which pass into the intestines of birds and insects and are given off with the excrements also pass finally into the earth.

Hansen has likewise shown that Sacch. apiculatus appears normally only on sweet juicy fruits and under the latter in the ground; the cause of this is the very slight power of resisting drying which this fungus possesses. Therefore, when present on the surface of unripe whole fruit, on leaves, twigs, etc., where it cannot multiply, it dies off after a comparatively short time through drying. Otherwise it