ZOOLOGY AND BOTANY, MICROSCOPY. ETC. 



471 



On looking througli the thnmb-nail with a direct-vision spectroscope 

 the first characteristic band is seen, sometimes accompanied by the second. 

 When a ligature is made round the joint the bands disappear, the yeUow 

 at the border of the ray D then slowly reappears, aad finally the bands 

 disappear entirely ; the time occupied is the time of reduction, and varies 

 between 25 and 90 seconds, the normal time being about 60 seconds 

 in health and in a state of rest ; it is connected with the quantity of 

 oxyhaemoglobin and the rapidity of exchange between the blood and the 

 tissues. 



Fig. 113 represents a hsematospectroscope with the lateral movements 

 which are required to study the phenomenon of the two bands ; it is 

 provided with a micrometric scale divided in wave-lengths. Fig. 114 is a 



Fig. 113. 



Fig. 114. 



double hsematospectroscope with a single slit by which two persons can 

 observe the same phenomena simultaneously. The form shown in fig. 115 

 allows the spectroscope to be placed horizontally. 



Experiment having shown that in the normal condition when the blood 

 contains 14 per cent, of oxyhsemoglobin the mean time of reduction is 



