710 ADVENTURES IN RADIOISOTOPE RESEARCH 



Growth and Renewal 



The nucleic acid formed during the course of the experiment, and for 

 that reason radioactively labelled (containing ^^P)^ is either to be found 

 in the newly formed tissue or to be attributed to the renewal of nucleic 

 acid already present. In the case of adenosine triphosphoric acid and 

 some other acid-soluble phosphorus compounds, renewal of the mole- 

 cules in the sarcoma and in other organs takes place at a very high rate. 

 These compounds exhibit radioactivity after the passage of only a very 

 short time when radioactively labelled phosphate is present. The nucleic 

 acid molecules, on the other hand, are only very slowly renewed in the 

 normal organs. Data on the speed of renewal of nucleic acid in the organs 

 of adult rats will be communicated shortly. 



We assume that the nucleic acid content of the sarcoma is proportional 

 to its weight or volume. This assumption is supported by the observations 

 which are discussed below. The percentage growth of the nucleic acid 

 content is then equal to the percentage volume increase of the sarcoma. 

 By means of the radioactive experiments, we determine the percentage 

 of nucleic acid molecules which have been formed in the period of 2 

 hours before the rat is killed and we ascertain the growth by studying 

 the volume increase of the sarcoma in the same period. The size, how- 

 ever, is too small to be ascertained by measuring the dimensions of the 

 sarcoma. The growth which has taken place in the last 24 hr, on the 

 other hand, can be measured and hence the growth occurring in the last 

 2 hr can be calculated. It seems to be more correct, however, to base 

 the calculation of the volume increase in the 2 hr period not on a single 

 measurement, which is affected by uncertainties (see Table 11), but to 

 use a series of measurements which have been made over the last 6 

 days of investigation. The results of these and other measurements 

 are to be seen in Tables 11 and 12.^^^ The latter table contains a summary 

 of the results obtained for sarcomas which weigh less and more than 

 40gm.The sarcomas studied by the radioactive methods were mostly 

 lighter than 40 gm and our interest is therefore more particularly in the 

 volume increase of this group of sarcomas. 



The dry weight of the sarcomas studied varied between 18.5 and 20.7% 

 (average 19.2%) of the weight of the sarcoma. 



It is readily appreciated that in sarcomas which have nearly attained 

 the limit of their possible growth, the daily percentage volume increase 

 is considerably less than in sarcomas which are able to grow to an almost 

 unlimited extent. The average content of nucleic acid per gm of sarcoma 

 in both cases, however, is found to be essentially the same; it amounts 



1 Values of 26.5 and 14.3, respectively, are obtained by calculating the percen- 

 tage volume increase of the sarcoma from measurements taken at the beginning 

 and end of the last day. 



