114 MUTATIONS 



via peroxide. The Texas school of workers found that mutations can 

 be produced in bacteria by irradiation of the medium on which they 

 are subsequently plated (69). When they analyzed this mutagenic 

 effect of irradiated medium, they found that the responsible mutagens 

 were amino acid peroxides. 



Thus, the group of peroxides forms a link with radiation muta- 

 genesis. Curiously enough, it seems that formaldehyde, at least in one 

 type of experiment, should be included in this group. Formaldehyde is 

 a very curious mutagen. In Drosophila, where Rapoport first dis- 

 covered its mutagenic action (58), it can be applied in two different 

 ways, and I think it acts quite differently when applied in one or the 

 other way. 



The first way, which was discovered by Rapoport, was to mix the 

 formaldehyde with the food of growing larvae. I shall come back to 

 this in a moment. The second method, which was introduced much 

 later (3), was to inject an aqueous solution of formaldehyde into adult 

 flies. This is similar to the way in which it is applied to Neuro- 

 spora (18), where spores are treated in an aqueous solution. Under 

 these conditions, formaldehyde seems to produce mutations by form- 

 ing peroxides with metabolically produced hydrogen peroxide. The 

 evidence is this: When Neurospora conidia are treated with hydrogen 

 peroxide, there is a very small mutagenic effect. When they are treated 

 with formaldehyde, there is again a small effect. When they are treated 

 with a mixture of the two, there is a very strong effect. Sobels (65) 

 in Holland found further evidence for this interpretation. He treated 

 Drosophila with the organic peroxide that is formed through the re- 

 action of formaldehyde and hydrogen peroxide, and it produced 

 mutations. 



When formaldehyde is mixed with the food of the Drosophila larvae, 

 it probably acts in a completely different way. It has a very specific 

 effect then. It acts only on growing spermatocytes. It does not act on 

 females at all, nor even on adult males. It acts only during one very 

 particular stage, occurring only in the growing larvae, where the devel- 

 oping spermatocyte increases tremendously in growth, and where, 

 presumably, very many synthetic processes are going on. In fact, 

 Alderson (1) showed quite recently that when the larvae are reared 

 on a chemically defined sterile medium, formaldehyde acts only in 

 the presence of adenosine riboside. Certainly this indicates that its 

 mutagenic effect is somehow connected with the synthetic processes 

 going on during the sensitive stage. 



I think that covers the main groups of mutagens. There is still 



