SELECTION AND PREPARATION OF ORGANISMS 65 



these difficulties is to select an animal or plant that is a common item 

 in commerce. If the pronghorn antelope and the sheep both show a 

 feature which is to be studied, then use the sheep. If cither wheat or 

 buffalo grass would be suitable, choose the wheat because seeds are 

 more readily available. The cost of the living material is to be considered 

 also. In some studies it is desirable to raise the experimental organisms 

 within the research facilities. Many laboratories maintain colonies of 

 mice, rats, or rabbits because they can produce more uniform animals 

 at any desired time. Many plant investigations are carried out with plants 

 that have been raised in a greenhouse, or better, in chambers where all 

 growth conditions can be carefully controlled. To summarize, then, an 

 organism for experimental purposes must be easily collected in the 

 vicinity of the lab, must be cheap, or must be susceptible to cultivation 

 or maintenance under artificial conditions. Lest it be thought that this 

 consideration is very obvious, let it be known that the present author 

 was once involved in a study using marine seaweeds in a laboratory in 

 Minnesota, more than a thousand miles from the nearest ocean. 



Durahility: Another less obvious essential feature of the experimental 

 organism is durability. Some animals or plants are better able to stand 

 the experimental treatments than others. If a certain organism is ex- 

 tremely susceptible to temperature changes, and it is impossible to main- 

 tain a constant temperature, perhaps another organism might serve as 

 well. If a long term experiment is planned, the natural life span of the 

 organism should be considered. Organisms occasionally confound an 

 experiment by dying anyway, and one would be foolish to increase the 

 likelihood of this disaster by choosing a fragile species. 



Desirable features 



General Knowledge of the Species: If either a well-known species or 

 a rare species can be used, the well-known species should be chosen. In 

 this respect, there may be some economic or political advantage in using 

 the well-known species. One of the reasons for using sugar beets in our 

 own laboratories is that the sugar beet is an important crop in our area. 

 It is somewhat easier to justify the expenditure of funds on sugar beets 

 than on dandelions. There is no benefit to be gained from the use of an 

 exotic species because it is exotic. 



Background Information: Some species of animals and plants have 

 been used for many studies in the past, and a great volume of informa- 



