128 



ANALYSIS OF THE ENVIRONMENT 



The presence of ultraviolet rays increases 

 the photopositive reaction of Drosophila 

 melanogaster and causes Paramecium, 

 which is indifferent to white hght, to be- 

 come photonegative. The stingless bee, 

 Triaona, can be trained to respond to ultra- 

 violet patterns invisible to the human eye 

 (Warden, Jenkins, and Warner, 1940). 

 These instances indicate that animals may 

 detect and react to ultraviolet radiation to 

 which man is totally blind. Flowers have 

 patterns in the ultraviolet, as well as the 

 familiar ones in the visible range. The ex- 

 tent to which these shorter wavelengths are 

 important to nonhuman animals, insects 

 particularly, in such matters as protective 

 coloration, mimicry, and sex recognition in 

 dimorphic species, is still an open question. 



Certain chemical syntheses appear to be 

 related to the photochemical eflFect of radia- 

 tions of short wavelength. More nitric acid 

 is found in the atmosphere at high altitudes 

 than would be expected from amounts pres- 

 ent nearer the earth. Irradiation of moist 

 air by ultraviolet greatly increases the 

 amount of oxides of nitrogen present, per- 

 haps as a result of oxidation of ammonia. 

 Formaldehyde can be detected in rain 

 water, which presumably obtains it from 

 the air, and may be produced from caibon 

 dioxide and water in the stratosphere by 

 irradiation with a wavelength of 2550 A at 

 altitudes where ozone absorption has not 

 eliminated this wavelength (Ellis and 

 Wells, 1941). 



Ultraviolet radiation is closely associated 

 with production of the antirachitic vitamin 

 D that is accomplished by irradiation of 

 certain sterols. This vitamin rarely occurs 

 in living plants, although it may be rapidly 

 formed by irradiation of dead plant ma- 

 terial. It is abundant in certain oils of fishes 

 and occurs widely among animals. We do 

 not vet know the source of the rich supply 

 in fishes. It has been suggested that vitamin 

 D is formed by insolation of plankton, 

 which makes up the food of many small 

 fishes, which in turn contribute their supply 

 to the lareer fishes that devour them. We 

 do know that ultraviolet ravs may penetrate 

 a considerable distance in sea water. 



The alga, Nitzschia closferUim, synthe- 

 sizes vitamin A. but not D. Zooplankters 

 contain ergosterol, but no vitamin D in the 

 spring; in midsummer they may also con- 

 tain this vitamin. If the fish get their rich 

 supply from irradiated animal planlcters. 



they must concentrate it with high effi- 

 ciency. At least a part of their supply may 

 be synthesized by the fishes themselves. 

 Irradiation of birds and mammals is the 

 source of much of their supply of vitamin 

 D. Irradiation of fishes, on the other hand, 

 whether done experimentally or naturally, 

 does not seem to be similarly effective. The 

 basking shark, Cetorhiniis maximiis, for 

 example, suns at the surface for hours at 

 a time, yet the vitamin D content of its 

 liver oil is low, although some of its non- 

 basking relatives have an unusually large 

 amount. 



Higher vertebrates lack the ability to 

 synthesize vitamin D; they must ingest their 

 supply or obtain it by the insolation of fats 

 on the integumentary surface. The skin of 

 many animals has a fairly good supply of 

 sterols, and all animal fats contain them. 

 Irradiated skin or fur or feathers, if oily, 

 are antirachitic; even the irradiation of the 

 feet is curative for rickety chickens that 

 have their preen glands removed. The 

 feathers and skin of the birds without preen 

 glands have little antirachitic power. In 

 licking fur, or in preening feathers, mam- 

 mals and birds secure irradiated oil. Carni- 

 vores apparently acquire their needed sup- 

 ply by eating the feathers and fur of their 

 prey, for the young of certain carnivores in 

 captivity require such material as a part of 

 their diet if they are to develop successfully. 



Carotinoids are widely distributed among 

 plants, and those found in phytoplankton in 

 general have vitamin A activity. The caro- 

 tene synthesized by algae is taken up by 

 animal microplankters, including minute 

 crustaceans. It can be used by animals as 

 a source of vitamin A that they can make 

 for themselves. Many mammals obtain 

 vitamins from the symbiotic bacteria pre- 

 sent in the alimentary tract. Thus, the cow 

 does not need pyridoxine (vitamin B«) in 

 its food, since its supply can be obtained 

 from the bacteria present in its extensive 

 stomach (Heilbrunn, 1943). 



Knowledge of the ecology of vitamins is 

 inadequate, and is based largely upon 

 observations on man and certain laboratory 

 vertebrates. Such information is by no 

 means final. Earthworms, snails, and other 

 invertebrates contain substances with prop- 

 erties like those of provitamin D, and it is 

 possible that this vitamin may be impor- 

 tant for many invertebrates as well as foi 

 vertebrates (Giese, 1945). 



