HYDRO -CARBONACEOUS PRINCIPLES. 39 



then in small quantities, in the structures of our domestic 

 animals. 



Carbonate of magnesia is rare in the tissues of animals. 

 It is found in the urine of herbivora, being derived from the 

 cereals, from which traces of it are to be obtained. 



It would appear that the widely diffused oxide, arsenic, is 

 removed from the bodies of animals with some difficulty, and 

 it has been regarded by some as a necessary principle of the 

 body, and the same may be said of lead. Arsenic readily 

 penetrates plants, and through them may, under certain 

 favourable circumstances, find its way into the systems of our 

 domestic animals. 



Free ammonia, which is supposed always present in the 

 blood, has been alluded to by Dr Benjamin Kichardson as 

 one of the most important proximate principles of animals, 

 inasmuch as to it is due the persistent fluidity of the vital 

 fluid. Some arguments and facts can be supported in opposi- 

 tion to Dr Richardson's views, but, according to him, it 

 is the proximate principle most readily separated from the 

 body, because escaping the moment the blood-vessels are 

 opened and blood drawn. In some diseases ammoniacal salts 

 exist in the blood, and it were interesting if their presence 

 could be demonstrated in the many disorders so suddenly 

 fatal in animals, and which depend on an almost instantaneous 

 change in the constitution of and tendency to coagulation in 

 the blood. 



The sulphocyanide of sodium referred to by Lehmann is 

 only found in saliva. Other chemists state it to be a sulpho- 

 cyanide of potassium, and not of sodium. 



HYDRO- CARBONACEOUS OR HEAT- GIVING PRINCIPLES OF 

 FOOD. The more we extend our knowledge on the nature 

 of food and the principles on which our domestic animals are 

 to be fed, the more must we recognise the importance of this 



