82 IMMEDIATE PRINCIPLES OF THE TISSUES. 



transformed in the organism into another, except, perhaps, that the 

 albuminose of the blood may be transformed into albumen. It 

 appears, however, that either of the organic principles taken in our 

 food, and subsequently changed by the digestive process, may afford 

 the materials out of which the same, or perhaps several others of 

 the organic substances, may be formed in the organism by the assi- 

 milative endowments of its respective parts and organs. Still less 

 can any tissue once formed be directly transformed into another, as 

 cartilage into bone, &c. Whenever this appears to be the case, the 

 former tissue is, in fact, replaced by the latter. 



All these substances are assimilable ; i. e. they do not appear in 

 the urine 1 if admitted into the blood from the alimentary canal or 

 otherwise, in proper quantity, but disappear entirely from the blood, 

 and become associated with the tissues. Even the organic substance 

 of bone (osteine), so long as it is associated with the phosphate of 

 lime, will sustain an animal. (Magendie.) The fluid obtained by 

 prolonged boiling of bone is, however, not capable of sustaining 

 animal life for a long .time, for thus the osteine is converted into 

 gelatine, which is not assimilated, but appears in the urine. 



But none of these organic substances, taken alone, can long sus- 

 tain life ; the principles of the first and second classes must be 

 added, as mere accessories, but, at the same time, indispensable. In 

 muscle, for instance, the musculine is united, though feebly, with 

 creatine and creatinine, besides the water and the salts. Nor can 

 any principle alone (not even the organic substances) form a sub- 

 stance manifesting a single vital property. If the fibrine of the 

 blood sometimes appears to do so, it is because the blood contains 

 the principles of all three classes ; for fibrine alone, though it may 

 form a false membrane (falsely so called), can never become vas- 

 cular. 



Thus we must distinguish between the organic principles on the 

 one hand, and the anatomical, or rather histological, elements of the 

 organism on the other. The former have no proper form. The 

 latter present the form of membrane, fibres, cells, &c., and are never 

 constituted of a single substance alone. The simple cell or mem- 

 brane contains principles of all the three kinds, water always exist- 

 ing in greater or less abundance, besides salts and other compounds. 



1 In diseased conditions of the kidneys, albumen may exist in the urine, as all 

 are aware. 



