cviii GENERAL SUMMARY OF SCIENTIFIC AND 



too high feeding is wasteful, and that, for milk richer in 

 butter or caseine, recourse must be had to different breeds 

 of cattle rather than to alterations in the composition of the 

 fodder. 



A most interesting feature of some of the feeding experi- 

 ments is the use of the so-called " respiration apparatus" de- 

 vised by Pettenkofer of Munich. Besides the one in use by 

 Pettenkofer, three others are already in operation in the Ger- 

 man experiment stations. The apparatus consists of a large 

 air-tight chest or compartment, in which the animal is kept 

 while under experiment. Arrangements are made for sup- 

 plying food and water, and for collecting the solid and liquid 

 excrement, while the supply of air is constantly renewed by 

 a current which is analyzed before and after j)assing through 

 the compartment, and thus the products of respiration are 

 determined. By this means the amount and composition of 

 the food, and of all the products of its transformation in the 

 animal's body, may be determined. From these data are in- 

 ferred the functions of the different food insjredients in the 

 animal economy. This method of experimenting is compar- 

 atively new and very complicated. It gives promise of re- 

 sults of great importance for the theory, of cattle-feeding. 



The most important experiments in vegetable nutrition 

 and growth may be divided into two general classes : those 

 performed in natural soils, as in gardens and fields, for the 

 purpose of observing the effect of different fertilizers and 

 methods of culture on the growth of different crops ; and 

 those in which plants are grown in artificial soils or in water*, 

 to which are added the various chemical elements found to 

 be taken by plants from the soil the object being to de- 

 termine which of these are essential to the growth of the 

 plant, and Avhat are the functions of each in the vegetable 

 economy. Knop, Sachs, N'obbe, Hellriegel, and Wolff are 

 among the most prominent in these investigations. Nobbe, 

 of the station at Tharand, in Saxony, has lately completed a 

 series of experiments upon the function of potassium in the 

 growth of buckwheat and rye. The plants were raised in 

 solutions containing all the essential ingredients of plant food, 

 except that, in some cases, potassium was omitted. The 

 plants grown with the full list of food ingredients were nor- 

 pial and healthy, while those deprived of potash were dwarfed. 



