SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 751 



is in the right. But the well-known experiment of placing a homoio- 

 thermic animal at thermal neutrality so that there is no inducement 

 for it to give out heat, with the result that it still does (Rubner and 

 Terroine & Trautman), is not favourable to the Newton cooling 

 law. Benedict again, working with abnormal weight/surface rela- 

 tions in man, such as occur in athletes or very obese men, in atrophic 

 children or in men without limbs, found greater variations from the 

 surface law than could be accounted for as experimental error. 

 Benedict; Pfaundler; and LeBreton were all led to speak of an active 

 protoplasmic mass, with which the actual surface might or might not 

 be in exact direct proportional relation. Terroine, while accepting 

 the notion of active protoplasmic mass to a certain extent, held that 

 it was just that factor which had been adapted to the surface, and 

 so remained firm in his conviction that the surface was all along the 

 dominant factor. One fact, indeed, seems to have remained quite 

 unmentioned in the various discussions which have taken place on 

 these subjects, namely, the rising metabolic rate of echinoderm, 

 molluscan and amphibian embryos. There the surface is moment by 

 moment getting smaller and smaller relatively to the increasing 

 weight of respiring protoplasm, and yet the metabolic rate, whether 

 expressed as gram calories produced per gram per hour, or oxygen 

 taken in or carbon dioxide eliminated per gram per hour, is steadily 

 rising. If the surface were always the responsible factor this could 

 not be taking place. It was indeed always a little difficult to under- 

 stand what the adherents of the first of the two views (namely that 

 "thermolyse" is the cause of "thermogenese") imagined to take 

 place during embryonic development, for in the early stages the 

 surface would be far greater in proportion to the weight than at any 

 other time during life, and the egg-cell would be hard put to it to 

 satisfy the heat-dispersing demands of its surface. Again, as Deighton 

 and many others have pointed out, if the metabolic rate of the higher 

 animals fell during embryonic development at the same velocity as 

 afterwards during post-natal life, the single egg-cell must have been 

 practically red-hot. That a peak on the curve must exist was over- 

 whelmingly likely a priori, and, as regards the toad, the pig, and man, 

 it has been actually found, but the existence of such a peak can hardly 

 be allowed for on the von Bergmann-Rubner-Richet-Terroine theory, 

 for, as far as we know, it is not associated with any considerable 

 changes of surface area, and on their views it would have to be. It 



