formed by putrefaction in the alimentary canal. With some few exceptions such as these, the elements enumerated above are found combined with one another to form compounds. The compounds, or, as they are often termed in physiology, the proximate principles, found in the body are divided into (1) Mineral or inorganic compounds. (2) Organic compounds, or compounds of carbon. A convenient practical method of grouping these proximate principles of the body and of food is the following: Inorganic Nitrogenous Organic Non-nitrogenous Water. Salts-e.g.chlorides and phosphates ofsodium and calcium. Proteins-e.g. albumin, myosin, gelatin. Fats-e.g. butter, fats of adipose tissue. Simple organic bodies--e.g. alcohol, chole- Many of the substances enumerated above only occur in small quantities. The most important are the inorganic substances, water and salts; and the organic substances, proteins, carbohydrates, and fats. It is necessary in our subsequent study of the principles of chemical physiology that we should always keep in mind this simple classification; the subdivision of organic substances into proteins, fats, and carbohydrates forms the starting point, the A B C, as one might say, of chemical physiology. I shall conclude this introductory chapter by giving a list of the apparatus and reagents necessary for a practical study of the subject, and some tables to which it will be often found convenient to refer. The following set of reagents conveniently contained in 4 to 6 oz. glass stoppered bottles should be provided for each two students :— Made by adding 994 c.c. of water to 6 c.c. of the concentrated hydrochloric acid of the British Pharmacopoeia. The following additional reagents will be required by those taking the advanced course: In addition to these, there should be kept in stock in the laboratory, to be given out for the lessons in which they are used, the following: Standard solution of uranium acetate or nitrate for estimating phosphates." 1 Mercury is dissolved in its own weight of strong nitric acid. The solution so obtained is diluted with twice its volume of water. The decanted clear liquid is Millon's reagent. 2 Ten grammes of picric acid and 20 grammes of citric acid are dissolved in 800 to 900 c.c. of boiling water, and then sufficient water added to make up a litre. 3 Made by mixing 1 volume of barium-nitrate solution with 2 of bariumhydrate solution, both saturated in the cold. * Prepared as follows:-Sodium acetate, 100 grammes; water, 900 c.c.; glacial acetic acid, 100 c.c. 5 Instructions how to make standard solutions will be given in the lessons where they are used. Apparatus which is not so frequently used, such as that employed in generating carbonic anhydride, carbonic oxide, or sulphuretted hydrogen, may be given out as required. The laboratory should also possess a good balance, with its accessories, water and air baths, kept at various temperatures, retorts, and analytical apparatus generally. The microscope, polarimeter, spectroscope, dialyser, are also frequently employed in chemico-physiological investigations. Apparatus and reagents for carrying out the Kjeldahl process are also necessary. WEIGHTS AND MEASURES The weights and measures usually employed in science are those of the metric system; but as in this country the practical physician still largely uses English grains and ounces, we may compare the two systems in the following way :— 1 grain Weights 1 ounce = 437.5 grains 1 lb. = 16 oz. = 7,000 grains = 453.5925 The scruple 20 grains = 1.296 gramme, and the drachm = 60 grains = 3.888 grammes, are retained in use, but neither is an aliquot part of the ounce; though for practical purposes an ounce is considered to consist of 8 drachms. The standard of length is the metre; subdivisions and multiples of which with the prefixes milli-, centi-, and deci-, on the one hand, and deca-, hectoand kilo-, on the other, have the same relation to the metre as the subdivisions and multiples of the gramme, in the table just given, have to the gramme, thus : 1 millimetre = = 0.001 metre 1 minim = 39.37079 99 Measures of Capacity (English System) 1 fluid drachm = 60 minims 1 fluid ounce = 8 fluid drachms 1 pint = 20 fluid ounces 1 gallon 8 pints = (Metric System) In the metric system the measures of capacity are intimately connected with the measures of length; we thus have cubic millimetres, cubic centimetres, and so forth. The standard of capacity is the litre, which is equal to 1,000 cubic centimetres; and each cubic centimetre is the volume of 1 gramme of distilled water at 4° C.1 The scale most frequently used in this country is the Fahrenheit scale; in this the freezing-point of water is 32°, and the boiling point 212°. On the Continent the Réaumur scale is largely employed, in which the freezingpoint is 0°, and the boiling-point 80°. In scientific work the Centigrade 14° C. is the temperature at which water has the greatest density. For practical purposes measures are more often constructed so that a cubic contimetre holds a gramme of water at 16° C., which is about the average temperature of rooms. The true cubic centimetre contains only 0.999 gramme at 16° C scale has almost completely taken the place of these; in this system the freezing-point is 0° and the boiling-point 100°. To convert degrees Fahrenheit into degrees Centigrade, subtract 32 and multiply by, or C=(F-32) §. Conversely, degrees Centigrade may be converted into degrees Fahrenheit by the following formula: F = £C +32. TENSION OF AQUEOUS VAPOUR IN MILLIMETRES OF MERCURY FROM 10° TO 25° C. The above atomic weights are taken on the basis that O=16; that of hydrogen will then be 1.008. |