412 NOTES. 



lived more than a year. However, so far as I know, no satisfactory 

 series of experiments have been carried out to the end. 



N'ote 10, page 43. Even the statements in handbooks (see Milne- 

 Edwards, Leqons cVAnatomie comparce, viii. 1G9, 184) or in special 

 treatises, as to the requisite maximum (or optimum) of the amount of 

 food, show great errors, because it is impossible to obtain by experiment 

 any perfectly satisfactory information as to the relations of consumption 

 and ejection. Thus Hermann says : ' Even far more uncertain are thq 

 statement s as to the absolute amount of the minimum of excretion or 

 the minimum of food required to cover it, in consequence particularly 

 of the uncertainty of the methods of inquiry formeily pursued ; ' and 

 he therefore forbears mentioning any absolute figure for the minimum 

 of assimilated matter, as ascertained by these methods. Moreover, the 

 .subject has never been, to my knowledge, treated from any more general 

 point of view than a purely medical one. Thus, for instance, the fact 

 that a kilogiamme weight in a pigeon needs more nutrition than the 

 same weight in a dog, and this, again, more than a kilogramme in a 

 man, is explained by a reference to the greater energy of the vital 

 processes in the smaller organisms. This argument is just, if it is con- 

 fined to the warm-blooded animals, but it is false with regard to the cold- 

 blooded animals ; for as, in these, the variations in the temperature of 

 the body agree perfectly, or very nearly, with those of the surrounding 

 medium, water or air, no more warmth need be produced in the small 

 animals than in the large, nor need a correspondingly larger amount 

 of nourishment be consumed. Beyond this we know absolutely nothing 

 of their relations in cold-blooded animals. 



Kote 11, J'a/i'fi 50. At p. 46 a similar example was mentioned, where I 

 pointed out that the assimilation of food in Lymncea stcxfinalis did not 

 depend merely on the circumstance of the food being obtainable in suffi- 

 cient quantity and of suitable composition, but also on the osmotic 

 action of the skin itself. If the temperature is too low, below 12° C. for 

 instance, assimilation ceases in these snails although they continue to 

 feed ; at 20° G. the greatest proportion of food is digested and the 

 most rapid growth attained. But even then, this only takes place 

 when the influence of the volume of water, which can only be exer- 

 cised by the osmotic action of the skin, is exercised in the most 

 favourable manner. For more details on this point see Chapter V. and 

 the notes. 



Ifule \1,x>a(je 60. For all who think that the number of cases men- 

 tioned in the text are insufficient evidence for the position here advanced, 

 I here briefly give a number of other similar ones. Eels, which usually 

 live on animal food, will also eat bread. Spiders feed almost exclusively 

 on Articulata; a few species, as our European Attjpns Suken, feed on 

 snails ; the tropical species of MygaU are said to eat small birds ; here 

 in Wiirzburg, I and Menge fed them with young mice. The Loach, 



