ANALYSIS OF OBGANISMS 169 



ether extract if the sample consists largely of adult females with many 

 embryos in their brood chambers. On the other hand, if the sample con- 

 tains a large proportion of immature individuals, or if it is made up of 

 females carrying relatively few embryos, the yield of ether extract will 

 be much smaller. 



In these eight samples of Daphnia pulex the crude fiber or chitin 

 varied from a minimum of 3.34 per cent to a maximum of 10.89 per cent 

 of the dry weight of the material, a little more than a threefold differ- 

 ence ; on an ash free basis the percentages range from 3.62 per cent to 

 13.08 per cent of the organic matter. The samples from Devils Lake 

 show a larger percentage of crude fiber than those from Lakes Monona 

 and Waubesa, the minimum of the former being larger than the maxi- 

 mum of the latter. 



Three determinations showed that only small amounts of pentosans 

 were present in the material, the maximum quantity being 1.92 per cent 

 of the dry weight of the sample. 



The nitrogen free extract ranged from a minimum of 8.25 per cent 

 to a maximum of 25.19 per cent of the dry sample; on an ash free 

 basis this extract constituted from 9.4 per cent to 31.34 per cent of the 

 organic matter. In other words the crude protein, the ether extract, 

 and the crude fiber account for approximately 70.0 per cent to 90.0 per 

 cent of the organic matter in these eight samples of Daphnia pulex. 



The percentage of ash also showed somewhat more than a threefold 

 variation, ranging from 7.62 per cent of the dry material in one sample 

 from Lake Monona to 25.85 per cent in one sample from Devils Lake. 

 The minimum percentage of ash in the five samples from Devils Lake is 

 16.87 per cent and this is exceeded by one of the samples from Lake 

 Monona; the other sample from Lake Monona as well as that from 

 Lake Waubesa gave a much smaller percentage of ash. An ash deter- 

 mination on a small sample of Daphnia pulex obtained from Devils Lake 

 on September 30, 1918, yielded 11.06 per cent; this is appreciably 

 smaller than the minimum noted above. 



The percentage of ash appears to bear some relation to the age of 

 the specimens in Daphnia pulex. By means of small platinum crucibles 

 and a sensitive assayer 's balance the amounts of organic matter and of 

 ash may be readily ascertained for small numbers of these organisms, 

 from 100 to 500 individuals being used for such determinations. In a 

 series of such samples taken from material collected in Lake Monona on 

 May 16, 1918, the largest females, noted as adults carrying embryos, 

 yielded 13.93 per cent of ash; medium sized individuals, estimated as 

 one-fourth to one-third grown, contained 18.89 per cent of inorganic 

 material, while the smallest size gave 23.6 per cent of ash. In two sam- 

 ples collected at Devils Lake, September 30, 1918, the ash amounted to 



