Dr. Mitchell on the Occurrence of Sugar in the Animal Economy. 97 



some such analyses, more as showing the necessity, in all analyses of blood, 

 for stating the point of the circulation from which the blood was drawn, 

 and the circumstances, as regards diet, under which the animal existed 

 at the time of the experiment ; I say more for these reasons, than that I 

 conceive them to have any practical bearing on the solution of the question 

 in hand. 



Three dogs were bled, each from the jugular vein and vena porta, and 

 the six portions of blood were analysed. No two of the analyses were 

 identical, but the differences all went in one direction ; and I give the 

 following as an average of the three : That from the jugular vein con- 

 tained in 1000 parts 769.21 of water and 230.78 of solids, while that from 

 the portal vein gave 726.54 of water and 273.40 of solids, showing an 

 excess of nearly 4 J per cent, in the solids of thex>ortal blood. (This excess 

 consisted mainly of the globules and fibrine.) These three animals had 

 been fasting some time before losing these specimens of blood; and I now 

 give you the average of five other experiments, in which the dogs, at the 

 time of death, were in active digestion of fluids and solids. In these, the 

 blood from the jugular vein gave, in 1000 parts 780.92 of water and 219.08 

 of solids, and the portal blood 790.11 of water and 209.89 of solids, 

 shoioing, under tliese altered circumstances, a loss of solids, where an 

 excess existed when the animals ivere fasting. The precaution, to which 

 I alluded, is surely inculcated in these results. 



I now would inquire if sugar exists in the same proportion in all classes 

 of animals, under conditions as similar as possible, and I find that in birds 

 and maminiferous animals the amount is alike very considerable. In 

 reptiles, such as the frog and lizard, the sugar existed merely as a trace, 

 while in fishes, as in the .skate and eel, not a trace could be found. 

 Whence comes this disappearance of sugar in cold blooded animals? Does 

 it arise from the diminished energy of the respiratory functions? 



This query leads us to the path, by diligently following which, I believe, 

 we shall arrive at the explanation of this important phenomenon. 



" Several circumstances have induced recent writers to conclude that 

 nitrogenised foods are alone capable of conversion into blood and of 

 forming organized tissues ; that, in fact, they only are the foods properly 

 so called, and hence have been denominated by Liebig the plastic elements 

 of nutrition. The non-nitrogeniscd foods, it is said, are incapable of 

 transformation into blood, and are therefore unfitted for forming living 

 tissues. They are, nevertheless, essential to health ; and Liebig asserts 

 that their function is to support the process of respiration, (by yielding 

 carbon and hydrogen, the oxydation of which is attended with the 

 development of heat,) and some of them, he states, contribute to the 

 formation of fat. These non-nitrogenised foods he calls Uie elements of 

 respnralion." 



It would appear, then, at all events possible tJiat respiration is actively 

 concerned in bringing ab&ut this destruction of tJie saccharine principle. 

 If so, we shall probably find some change in the expired air, a diminution 



Vol. Ill— No. 2. 3 



