J. Alan Murray 109 



liO per cent, of the live weight. This estimate was based on the increase 

 ill basal katabohsm, determined by Armsby("'), in an ox. Pigs probably 

 have a smaller capacity for food than ruminants of the same size; but, 

 on the other hand, the food which is customary and suitable for them 

 has a much higher productive index (ratio of dynamic to total energy). 

 It was recognised that the result depends upon these factors and that 

 any animal would require an indefinite time to attain the maximum 

 degree of fatness of which it is capable under any given conditions. The 

 fact that over 60 per cent, of body fat was recorded in two cases in 

 Swanson's data indicates that the theoretical maximum is probably 

 higher for pigs than for ruminants. At any rate it disposes of the objec- 

 tion that the estimated maximum (60 per cent.) is far beyond what had 

 hitherto been recorded. The theoretical minimum of body fat is zero. 

 The lowest recorded in the data under consideration is 5-27 per cent, in 

 the pigs and 3-64 per cent, in the ruminants. There is no reason to 

 believe that these records are the lowest attainable in living animals. 



Attention may be called to the fact that the diminishing percentage 

 of water in the non-fatty matter coincides with diminishing rate of 

 growth and to the possible connection between these phenomena. The 

 biological significance of the constants in the formula for water may also 

 prove a matter of interest to pliysiologists. 



Summary. 



Animal bodies are composed of fat and non-fatty matter. The relative 

 proportions of these two ingredients vary within wide limits but can be 

 controlled by food. The non-fatty matter consists of water, protein and 

 ash. The percentage of water varies with the age of the animal in a 

 definite manner. This has been determined with tolerable certainty for 

 cattle. The available evidence indicates that the same formula is applicable 

 to pigs and, with .slight modification, also to sheep, but these inferences 

 require confirmation. The ratio of protein to ash is the same in sheep 

 as in cattle but in pigs it is higher. In any case it does not alter with 

 the age of the animal but it may be influenced to a certain extent by 

 the food. Individual variation is wider in pigs than in ruminants. The 

 average composition of the whole body at any stage can be calculated 

 when the live weight and percentage of fat in it are known. 



