THE PRINCIPLE OF VITAL AFFINITY. JJ07 



of carbon and hydrogen. The composition of most fats is stated by Liebig to be 

 Cij H,„ Oi ; and we have thus, therefore, another compound formed apparently by 

 vital affinity, indicating a peculiar attraction of the two first elements for one an- 

 other, and a feeble attraction for oxygen. Indeed, in the composition of wax 

 (one of this family of compounds), as stated by Muldee, the proportion of oxygen 

 is only one equivalent to 24 of carbon ; in cholesterine, the proportion of carbon 

 to oxygen is stated as high as 36 to 1 ; and in many volatile oils, no oxygen has 

 been detected. 



Supposing such a peculiar affinity to act, there is obviously no difficulty (on look- 

 ing at the numbers indicating the proportions of the elements) in understanding the 

 formation of these compounds out of starch (d,. Hi„ Oi„), just as there is none 

 in understanding the formation of starch or sugar (although by an affinity occur- 

 ring only in living bodies, and which we regard as vital) from carbonic acid and 

 water (CO2 + HO), in living vegetables, where a continual evolution of oxygen 

 attends the growth ; particularly if we suppose that the carbonic acid taken in 

 by the leaves and roots, is carried to, and decomposed in, all parts of the plant : 

 the formation of the fatty compounds, is, no doubt, one of the processes by which 

 the oxygen is set free. But in the case of animals, where (with the exception of 

 some of the infusory tribes") there is no evolution of oxygen, the formation of 

 fat from starch presents a difficulty. Yet the numerous observations and expe- 

 riments of Liebig and of Cheveeul and Milne-Edwaeds, leave no room for 

 doubt that various animals, fed chiefly on varieties of starch, or bees fed on sugar, 

 form a much larger quantity of fat, oil, or wax, than they have received mixed 

 with their food, and this when they are exhaling no pure oxygen, but, on the 

 contrary, compounds of hydrogen and carbon with oxygen, viz., water and carbonic 

 acid. Indeed, Dr Robert Thomson having ascertained by repeated experi- 

 ments, that the quantity of butter yielded by cows bears no fixed proportion to 

 the quantity of oleaginous matter contained in their food, varying indeed from 

 one quarter to nearly the whole of the oleaginous ingesta, thinks himself justified 

 in inferring that " the butter cannot be supplied from the oil of the food." (On 

 the Food of Animals, p. 156.) 



It is quite certain that in this action, in all animal bodies, the greater part of 

 the oxygen of the starch employed must unite with a portion of its carbon and 

 hydrogen, and pass off in the excretions just noticed, leaving the small remainder 

 of the oxygen in combination with the predominant quantities of carbon and hy- 

 drogen. 



It appears possible, indeed, that all the oxygen which must be separated 

 from starch before it can be converted into fat, may be evolved in combination 

 with part of the carbon and hydrogen of the starch, without any constituent of 

 the air taking any part in the process ; but the quantity of fat formed would 

 then be small, and it is also possible that the oxygen of the air may be concerned 



