912 



ADVENTURES IX RADIOISOTOPE RESEARCH 



Table 1. 



Amount of Zinc Taken up by Neurospora 



200 /^gm/1. as recommended by Ryan et al. (1943) or 450 /^gm/1. as sta- 

 ted by Mitchell and Houlakan (1946). 



Figure 1 shows the very pronounced increase in weight of the mould, 

 from 71 to 100 and 159 mgm, after the addition of 2.5 and 12,5 mgm 

 of zinc respectively to the culture sokition. In experiments of shorter 

 duration the effect of zinc on the increase in weight was still more pro- 

 nounced (Fig. 2). After 48 hr 28 mgm were obtained in the absence of 

 added zinc, while adding 30 ^gm of zinc to a 150 ml. culture produced 

 83 mgm of mould. 



After 5 hr, a 150 ml. culture solution containing 2.5 //gm zinc produced 

 100.3 mgm and one with 12.5 /^gm zinc, an almost maximal weight of 

 158.9 mgm. In the former case 1 mgm Neurospora contained 0.015 figm 

 zinc; in the latter roughly twice that amount (0.035 /^gir). An increase 

 in the zinc content of the culture solution to 2000 jWgm did not increase 



