2o0 



THE INFLUENCE OF THE COOLING POWER OF. THE 



AT.MOSl'HEKE ON THE KATE OF GROWTH OF 



YOUNG ANIMALS. 



BY 



Eustace H. Cluver, M.A., M.D., B.Cii. (Oxon.), 



Professor of I'Injsiologij, University of the Witu-atcrsrand. 

 Johanneshunj. 



Bead July 10, 1922. 



The various forces inliueueing the growth of young animals 

 may be- grouped under two headings : an internal factor which 

 has been termed the growth impulse, and an external or nutri- 

 tional factor. The growth impulse is complex, and it is as yet 

 impossible to resolve the multiplicity of factors concerned. It 

 represents the power to grow inherent in the ferilised ovum, in 

 which must be pre-determined the extent to which such important 

 factors as endocrine secretions and " tissue tension "' will 

 function in the growing organism. 



For the complete development of the fertilised ovum to take 

 place — that is, for the perfect growth pre-determined by the 

 grow^th impulse to result — there must be ideal conditions of the 

 external or nutritional factor. The growth impulse would be 

 entirely ineffective if the external factor were absent. Thus an 

 acoiTi with the gro\^-th impulse to produce an oak Mould remain 

 an acorn if kept in an atmosphere of nitrogen. This external 

 factor is also multiple, and represents the sum of those external 

 factors which influence growth. Important amongst these are 

 (1) the nature and amount of the food presented to the young 

 animal; and (2) the atmospheric or climatic conditions to which 

 the young animal is subjected. 



It is evident that for ideal growth to take place the food 

 supply must not only be adequate, but must contain the ingre- 

 dients necessary for the manufacture of the various tissues of the 

 animal. Further, it has been established that, in the absence of 

 certain accessory substances or vitamins, these ingredients cannot 

 be built into the structure of the body. All three known vitamins 

 are necessary for normal nutrition to take place; but it would 

 appear that two of them are more particularly necessary for the 

 incoi-poration of the ingredients of food in the body of the young 

 animal, re.sulting in the growth of that animal, to take place. 

 These are the fat-soluble A and the water-soluble b vitamins.** 



Of the atmospheric conditions which may influence growth, 

 two have received attention : the atmospheric pressure, and the 

 cooling power of the atmosphere. It has been suggested that 

 prolonged exposure to the low atmospheric pressures obtaining 

 at such high altitudes as in the settlements in the Andes result 

 not only in an increased manufacture of red blood corpuscles, 



•These numbers refer to the papers listed in the References. 



