the spectrum, and was least of all in the infra-red. The protection of the tissues 

 of the reptile body by the corneous part of the integument against penetration of any 

 kind of solar radiation is thus extremely efficient. 



These measurements were made with the subject under investigation near the 

 exit slit of the spectrophotometer, at a distance of 4.5 cm from the window of the 

 phototube. In a second series the subjects were placed much closer to the photo- 

 tube (1cm distance). The ray that reached the object was thus much more concen- 

 trated. In consequence all readings gave higher transmission (up to 100%), but the 

 general picture remained the same. The readings in this second series gave approxi- 

 mately maximum values at right- angle incidence to the rays, which in nature would 

 be an extremely unusual occurrence. The first series is certainly a better illustra- 

 tion of what actually occurs in nature. Absorption of heat at the actual angles of 

 ray- incidence may be even lower than in the first series. The peak of transmission 

 at 1200/x in all the objects tested led to a further exploration of the 1000 to 14000/i 

 region, using Beckman I. R. 2 (sodium chloride optical apparatus). These results 

 show a second peak at 5400/i and deep depressions at 3000 and 6000/i' The first of 

 these may be produced by an OH- bond; the second may be due to the presence of 

 water. 



From the results of the experiments it is perfectly clear, that the fur and fea- 

 thers of mammals and birds are quite sufficient to prevent any transmission of the 

 ultra- violet and visible rays of the solar spectrum to the integument. The degree 

 of transmission in the infra-red, low as it probably is, deserves further study. Yet 

 these qualities of fur and feathers are certainly no special adaptation of desert ani- 

 mals, but hold good for mammals and birds in all biotopes. 



The study of these problems is still very much at its beginning. The physio- 

 logical consequences of the colour and structure of the integument, the importance 

 of the angle at which radiation meets the integument, etc. need much detailed re- 

 search. One point only is clear: the integument is normally fairly well protected 

 against penetration into its living tissues, irrespective of colour. For the time 

 being we would stress not the differences observed in our various objects, but the 

 striking similarity in the transmission trend through all colours and integumental 

 structures. The two peaks of transmission at 1200 and 5400/z, and the two depres- 

 sions at 3000 and 6000/i, as well as the general non - transmittance of ultra-violet 

 rays are probably due to certain biochemical components common to the integuments 

 of all animals. 



167 



