276 HENRY H. DONALDSON 



In general the loss of water in passing from the room-dried 

 to the oven-dried state is about 8.3 per cent of the room-dried 

 value, and the oven-dried weight is therefore 91.7 per cent of 

 the room-dried. Table 19 gives the several values, according to 

 the part of the skeleton, as determined for the four body-weight 

 groups which have been selected. 



It is possible, therefore, from these table values to make an 

 approximate determination of the weight of the skeleton or its 

 parts in one state of dryness, if the weight in the other state is 

 given. 



The most peculiar feature of this table, however, is the fact 

 that in no part of the skeleton is the percentage loss in the body- 

 weight groups from 4 to 50 grams essentially different from that 

 found in the heavier groups — despite the fact that in the first 

 group calcification is far from complete in any of the bones and 

 also tends to progress as the bones become older and heavier. 

 The full explanation of this result has not yet been obtained, 

 but some incidental tests indicate that in the room-dried state 

 both the salts found in bone and the collagen retain nearly a like 

 proportion of water, which is lost at 96°C. 



LENGTHS OF BONES 



It has been thought worth while to tabulate the lengths of 

 the long bones of the limbs during growth, in order to obtain the 

 relations between (A) the body weight or (B) the body length of 

 the rat, and the lengths of the respective limb bones, and also 

 to get an idea of the manner in which the lengths and weights of 

 the bones themselves change. For comparison with the data 

 from man these determinations are especially useful. 



A. Lengths of bones on body weight 



With a dial calipers measuring accurately to 0.1 of a milli- 

 meter, the lengths of the long bones, humerus, ulna, radius, 

 femur, and tibia were taken in the fresh, room-dried, and oven- 

 dried condition. 



