202 GROWTH OF PARTS AND ORGANS 



To present the results in a convenient form the organs have 

 been grouped in the text accordmg to the manner of their growth, 

 and in most cases the description is accompanied by a chart 

 showing the original data and the graph based on these data. 



In each case reference is made to the formula or formulas on 

 which the graph is based, but as a matter of convenience, the 

 formulas utilized for the graphs are grouped in the section 

 entitled "Formulas," pp. 282-298. 



The charts serve to show the form of the graph of growth in 

 each instance, but the precise weight values of the organs are to 

 be read from the tables. For those who desire to find the weight 

 of an organ in a rat of any body length or body weight a series of 

 values — computed by the aid of the appropriate formulas — ^are 

 given in tables 144-150 inclusive and in 152 and 153. 



In making these tables the determinations for the correspond- 

 ing body weights for each millimeter of length in each sex were 

 first made by formulas (5 a) and (5 b) and the body weights so 

 obtained were then used in computing the weights of the several 

 organs. 



In table 151 for the thymus however, it was found necessary to 

 enter the weight values of the organ according to the age of the 

 rat. 



In table 152 the computed weight of the thymus on body weight 

 is given on the assumption that the body weights are normal to 

 age in conformity with the data in table 157. 



2. Measurements. — Methods of examination and graphs. Unless 

 otherwise stated the following determinations were made on 

 stock Albinos taken from the colony at The Wistar Institute. 

 The animals were killed with chloroform twenty hours after the 

 last feeding and were dissected according to a fixed procedure. 



3. Body length on body weight. Technic: Immediately after 

 killing the rat was laid on its back and gently extended— the 

 tail being drawn out straight. With jointed cahpers the dis- 

 tance from the tip of the nose to the tip of the tail was taken and 

 its values in milhmeters found by applying the points to a scale. 

 Next the distance from the tip of the nose to the center of the 

 anus was found and its value in millimeters determined m the 



