n. A. SCHNRIDERMAN 55 



opment. Part of this problem is morphogenetic in character and demands solu- 

 tion in morphological terms. Is the change in terminal oxidase coincidental, 

 or is there an obligatory coupling between the function of the cytochrome 

 system and the actual development of the insect? A partial answer to this ques- 

 tion is provided by observations on the effects of carbon monoxide on the 

 growth of Cecropia. 



As in the respiration experiments, carbon monoxide's effects on growth were 

 appraised at positive pressures in transparent pressure chambers. The results 

 revealed that embryos, larvae and adults were killed by less than 5 days' ex- 

 posure to 20:1 CO/O2. Diapausing pupae, by contrast, survived at least 21 

 days' exposure to CO/O2 as high as 33*. i. This was not simply due to the pupa's 

 ability to withstand anoxia, since the maximum o.xygen debt that the pupa 

 could sustain was about 1000 Ml/grn live weight, and more than 3 days' exposure 

 to pure nitrogen was lethal. Nor was this CO-resistance characteristic of the 

 pupal stage generally, for non-diapausing pupae like GaUeria were killed by 

 carbon monoxide (32, 36, 40). 



The ability to survive in the presence of carbon monoxide persists throughout 

 the early stages of adult development. When a developing postdiapausing 

 Cecropia was exposed to suitable pressures of carbon monoxide, development 

 immediately ceased, but the animal continued to live. Carbon monoxide, in 

 effect, enforced an artificial diapause. As soon as the animal was removed from 

 carbon monoxide it resumed its development where it had left off and produced 

 an essentially normal adult moth. From this experiment we learn that carbon 

 monoxide inhibits an enzyme necessary for growth but apparently not for the 

 maintenance of the insect. This carbon monoxide-sensitive enzyme could be 

 cytochrome oxidase or tyrosinase. 



Conclusive proof that cytochrome oxidase is the target of carbon monoxide 

 was provided by reversing its inhibition of adult development with light (36). 

 Animals that had just initiated adult development had the opaque cuticle 

 overlying the anlagen of the genitalia removed and replaced by transparent 

 plastic windows. They were then compressed with carbon monoxide (CO/O2 

 = 20: i) and half the animals were maintained in darkness while half had their 

 windows illuminated. After 5 days the animals were compared with controls 

 kept in air. The illuminated genitalia had begun developing into adult organs, 

 while the unilluminated animals had not progressed. This difference was par- 

 ticularly striking at the anterior and posterior ends of the illuminated animals: 

 the illuminated gentalia showed considerable progress in development, whereas 

 the unilluminated facial region showed no morphological advance (cf. 55). 



These experiments assure us that the target of carbon monoxide in our 

 studies is cytochrome oxidase and that the absence of growth is due to specific 

 inhibition of cytochrome oxidase. Moreover, the experiments show that carbon 

 monoxide and light afford a remarkable tool for the student of growth. With a 



