ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 569 



degree that the adult toad thus distinguishes it. Substances of unusual 

 character and odour, when associated with food, do not stimulate the 

 olfactory organs in such a manner as to bring the toad to refuse the 

 food. The presence of such substances in close proximity to the toad, 

 and invisible because of darkness, are not repellent in effect on the toad. 

 Odour-streams specific in character, made to flow over and into the 

 nasal openings, stimulate the olfactory sense-organ, such stimulation 

 causing definite motor activities to follow. Appropriate operations are 

 confirmatory that the stimulation by such odour-stream is olfactory. 

 Section of the olfactory tract inhibits the reactions. Olfactory stimula- 

 tion and reactions are not affected by section of the ophthalmic branch 

 of the trigeminal nerve. Under circumstances allowing discrimination 

 the tadpoles of the toad prefer animal foods. Such discrimination 

 appears to rest upon the appropriate stimulation of the olfactory receptor. 

 Tadpoles of the toad show by proper reactions that animal food is 

 recognized, although not visually perceptible. The receptor organ so 

 stimulated must be a distance receptor, and thus is olfactory in function. 

 In the metamorphosed toad the visual stimulus is the principal and 

 guiding factor in procuring food. Therefore, it is inhibitory in relation 

 to other stimuli and their resultant reactions. 



Relation between Temperature and Standard Metabolism.* — 

 August Krogh has experimented with frogs and a young dog with re- 

 ference to the quantitative relation between temperature and standard 

 metabolism. It is important to distinguish the influence through the 

 nervous system from the direct influence on the rate of metabolism in 

 the tissues. When an organ is resting, a certain amount of meta- 

 bolism, the " basal " metabolism, continues to go on. There is a slow 

 spontaneous disintegration of the unstable bodies, the explosion of 

 which by nervous impulse constitutes activity. The influence of the tem- 

 perature upon the rate of spontaneous disintegration is a fundamental 

 problem, but it is difficult to secure the condition of basal metabolism 

 for a long enough time. The author has studied what he calls 

 " standard " metabolism — an approximation to the basal metabolism. 

 It is obtained when no assimilation of food is taking place, when move- 

 ments are prevented, and muscular tone either abolished or brought 

 down to a minimum. The absorption of oxygen has been used as the 

 index of the metabolism. 



When animals are studied under the "standard" conditions — all 

 nervous influences being abolished — the influence of temperature on 

 the metabolism of an animal is regular and constant, and can be ex- 

 pressed in a definite curve, which is not a straight line and cannot- be 

 expressed either by Arrhenius's formula or by the rule of van't Hoff. 

 The curves obtained for frogs and goldfishes and, in a single experi- 

 ment, on a young dog are identical, while that for pupa? of mealworms 

 is distinctly different, though of the same general type. 



Relation between Temperature and Respiratory Exchange in 

 Fiskes.f— Richard Ege and August Krogh have tested the applicability 



* Internat. Zeitschr. rhys.-Chem. Biol., i. (1914) pp. 491-508 (5 ligs.). 

 + Internat. Rev. Hvdrobio]., 1914, pp. 48-55 (3 figs.). 



Dec. 15th, 1915 ' 2 r 



