484 



excretion of carbonic acid by tlic animals during- tlie day-time was 

 different from that during tlie night, but that tliis was determined, not 

 by the amount of light and darkness, but by the distribution of food 

 during the two portions of the twenty-four hours. The feeding M^as 

 generally followed very soon by the excretion of carbonic .acid. The 

 excretion of water by the skin followed much the same rules as that of 

 the carbonic-acid excretion. A parallelism was found between the ex- 

 cretion of the carbonic acid and of the water in twent3"-four hours, both 

 being greater or less as the consumption of nutriment or respiration 

 material was greater or less. From this it would appear that, to econo- 

 mize food, it is necessary to protect animals from conditions which induce 

 perspiration. 



A certain medium temperature of the stall in which the animal is fed 

 will be the most economical, since, while the lesser heat involves the 

 necessity of a greater amount of food, an increased temperature, on the 

 other hand, produces an increased consumption of water, and, in conse- 

 quence, the increased transudation of water through the skin of the 

 animal, produces a loss of heat of the body by conduction and radia- 

 tion. 



The result showed that the food consumed was slightly greater than 

 that required to keep the body in statu quo along with a normal growth 

 of wool, but not to an extent which had any real significance. The 

 atmosphere contributed only one-sixth part to the material received, 

 but, on the other hand, laid claim to nearly one-half of the material 

 excreted. More than one-half of the organic substance of the food fell, 

 directly or indirectly, to the process of respiration, while the growth of 

 new wool absorbed not one per cent, of it. About eight-ninths of the 

 Tesidue were found in the ffeces and one-ninth in the urine. 



The oxygen excreted in the form of carbonic acid was nearly 

 -equal to that removed from the atmosphere, which is a general charac- 

 teristic of herbivorous animals. The distribution of various mineral 

 <3onstituents of food, on their reappearance in the fteces and urine, 

 corresponds, on the whole, though not exactly, with their respective 

 solubilities and dyalitic relations. The two alkaline earths, lime and 

 magnesia, appeared in relatively large proportions in the faeces — the 

 lime in greater proportion than the magnesia. Similarly with the two 

 alkalies and the urine, the potash was recovered therefrom in greater 

 proportion than the soda. Of the phosphoric acid scarcely more than 

 a trace was found in the urine. 



HiTMATE OF A:\rMONiA. — It has already been observed that i)lants 

 grown on soil rich in silica and poor in humus contain less silica in 

 their ash than those grown on soil poor in silica but rich in humus. 

 Since an excess of silica is always present in soil, the amount taken up 

 by a ])lant must clearly depend on other circumstances than the quan- 

 tity at its disposal. Thenard has recently thrown light on the subject, 

 by showing that humic acid forms, with ammonia and silica, very per- 

 manent acid com])Ounds. These compounds are soluble in very dilute 

 alkali, from whicih solution they can be separated unchanged. They 

 lose nitrogen only at a high temperature. ITumic a(;id does not com- 

 bine -svith silica unless ammonia be present. It appears probable from 

 these considerations that humic acid plays an important part in the 

 economy of plant-growth. When seeds germinate on wet blotting- 

 paper, a brown zone, having the reactions of humus, forms at some dis- 

 tance from the seed. The author concludes that humus is produced in 

 this case from a soluble colorless body by the action of the atmosphere. 



