78 CHEMICAL COMPONENTS OF THE HUMAN BODY. 



ing to M. Bernard, to predict the amount of sugar that will be secreted, accord- 

 ing to the depth of the incision. On the other hand, if the injury thus done be 

 too great, or if a violent electric shock be transmitted through the medulla ob- 

 longata, or any other severe lesion be inflicted on the nervous system, the pro- 

 duction of sugar is suspended ; and it appears that the same suspension may 

 occur as a result of diseases which produce a diminution of nervous power. 

 Division of the pneumogastric nerves usually prevents the irritation of the 

 medulla oblongata from exerting its usual effect, and even checks the production 

 of sugar when it has already appeared in the urine ; but this result is by no 

 means constant. The duration of the presence of sugar in the urine after the 

 operation is variable, according to the animal experimented on and the method 

 employed ; in general, it lasts forty-eight hours in the rabbit, and four days in 

 the dog ; but in one dog it continued for as much as seven days. The animals 

 are extremely restless during this period; the respiratory movements are 

 hurried ; the arterial blood presents almost a venous tint ; the quantity of car- 

 bonic acid given off is augmented ; nevertheless, the temperature of the body is 

 diminished several degrees. 1 



48. In close relation with the Sugars, both chemically and physiologically, 

 stands Lactic Acid, the presence of which, as a normal element of the blood, 

 and as performing very important functions in the economy, may now be re- 

 garded as well established ; and it will be conveniently considered here, although 

 it might be in some respects more appropriately placed in the category of excre- 

 mentitious matters. This substance, in its most concentrated state, is a color- 

 less, inodorous, thick, syrupy fluid, which cannot be solidified by the most intense 

 cold, dissolves readily in water, alcohol, and ether, has a strongly acid taste and 

 reaction, and displaces not merely volatile acids, but even many of the stronger 

 mineral acids, from their salts. With bases it generally forms neutral salts, all 

 of which are soluble in water ; but the alkaline lactates, and some others, cannot 

 be made to crystallize ; being only brought, by the greatest concentration, to the 

 condition of syrupy fluids. The composition of this acid is considered to be 60, 

 5H, 50; and it thus bears a close relation to that of Sugar, being exactly half 

 one equiv. of anhydrous Sugar-}- one equiv. of Water. It is, in fact, from sugar 

 or starch that it is most directly produced ; being the result of a new arrangement 

 of the atoms of these substances under the influence of an azotized ferment, as 

 when milk is turned sour by the action of its casein upon its sugar. But an acid 

 may be extracted from the " juice of flesh/' which, whilst apparently identical in 



1 This last fact appears at first sight to stand in marked opposition to the chemical 

 theory of Animal Heat ; but the Author would suggest that the following may be its ex- 

 planation. The production of heat being dependent upon the combustion (or union with 

 oxygen), not merely of carbon, but of hydrogen, and the amount of heat disengaged by 

 the combustion of hydrogen being much greater than that given off by the combustion of 

 its equivalent of carbon, we might expect that the conversion of a fatty substance, which 

 is almost entirely composed of hydrogen and carbon, into water and carbonic acid, shall 

 give off a far larger amount of heat than the combustion of a farinaceous or saccharine 

 substance, in which there is only carbon to be burned off, the hydrogen being already 

 united with oxygen in the proportion to form water. Experience shows that such is the 

 case ; for in the Arctic regions, ordinary bread is found to be very inefficient for the main- 

 tenance of animal heat, although an ample supply of oleaginous matters is completely effect- 

 ual for this purpose ; and, as Sir John Richardson has informed the Author, it has been 

 recently found by the Hudson's Bay traders, that maize bread, which contains a considera- 

 ble proportion of oil, is a most supporting food. Consequently, when the production of 

 fat by the liver is suspended, and the production of sugar takes its place> the amount of 

 heat generated by the consumption of even an augmented quantity of the latter, will not 

 be equal to that resulting from the combustion of the former ; for only carbon will be 

 burned off in the one case, whilst both carbon and hydrogen were consumed in the other. 

 The above account of the researches of M. Bernard is derived from the sources already 

 referred to ( 40, note). 



