Il6 ANIMAL CHEMISTRY LECTURE V. 



the agency of acids and alkalies, as well as by its post-mortem 

 putrefactive decomposition, and its ante-mortem natural trans- 

 formation, compounds belonging to both the aromatic and fatty 

 class simultaneously make their appearance. 



(124.) Among these compounds, leucine and tyrosine de- 

 mand our special attention leucine being an ammoniated term 

 of the 6 -carbon fatty, and tyrosine an ethyl-ammoniated term of 

 the 7 -carbon aromatic acid group. These two bodies occur in 

 association with one another under the following circumstances : 

 In the first place, they result from the putrefaction of flesh, 

 cheese, white of egg, gluten of wheat, &c. They have also been 

 detected in fresh blood, and occur very generally in glandular 

 tissue and secretion leucine, however, in much the larger pro- 

 portion, so that in some cases where it has been recognised, the 

 tyrosine probably accompanying it has been overlooked. Leu- 

 cine, more particularly, has been found in the spleen, thymus, 

 thyroid, and lymphatic glands ; and, indeed, from its occurrence 

 in the two former, received at one time the names of lienine and 

 thymine. Both compounds are met with most abundantly in the 

 pancreas and its secretion, but they also occur in the liver and 

 bile, and in the kidneys and urine, particularly in certain patho- 

 logical conditions. Leucine has also been recognised in the 

 salivary and intestinal glands and their secretions, and is, accord- 

 ing to Boedeker, an ordinary constituent of pus. 



(125.) That leucine and tyrosine pre-exist in the living body, 

 and are not merely post-mortem products, is evident from the 

 circumstance of their having been detected in the urinary, pan- 

 creatic, and, in the case of leucine, purulent and salivary secre- 

 tions of living animals. But more than this. A long time back, 

 De la Rue noticed that tyrosine existed pre-formed in the dried 

 cochineal insect ; and Staedeler, by crushing up various living 

 animals in a mortar with a mixture of powdered glass and alcohol, 

 has recently recognised the presence of both tyrosine and leucine 

 in invertebrata belonging to all the principal non-infusorial 

 classes. Thus it is manifest that leucine and tyrosine are pos- 

 sessed of a very extensive natural distribution. As yet indeed 



