9] VITAL IMPORTANCE TO MANKIND 265 



The lower plants come notably into their own as sources of drugs : 

 penicillin, streptomycin, aureomycin, Chloromycetin, terramycin, 

 and others recently developed from Fungi and their allies are being 

 found extremely valuable in the treatment of some of the most 

 severe diseases. Ergot, produced from the common fungal disease 

 of cereals bearing the same name, has long been known and is used 

 in the treatment of haemorrhages. Agar, widely obtained from a 

 number of Red Algae, is employed medicinally to prevent constipa- 

 tion, as well as industrially in food, paper, and cosmetic manufacture, 

 and as a culture medium for P'ungi and Bacteria. Algin, a product 

 of the larger Kelps, is used in a variety of cosmetics, foods, drugs, 

 and as a sizing for paper; these Brown Algae are also important 

 as sources of iodine and potash. 



Fatty Oils and Waxes 



Fatty or fixed oils are those which, unlike the essential oils (see 

 pp. 274-5), ^o riot easily evaporate, and so cannot be distilled without 

 becoming decomposed. Those which are liquid ' oils ' at ordinary 

 temperatures become solid ' fats ' on cooling, even as fats become 

 oils on sufficient warming. Like animal fats, they consist of glycerin 

 in combination with a fatty acid, and form soaps when boiled with 

 alkalis. Fatty oils (as they may in general be termed) are produced 

 in considerable quantities by many different plants, often being 

 stored in seeds for use in germination. Of them four main classes 

 may be recognized, as follows : 



1. Drying oils, which on exposure dry into thin elastic films 

 and are of great importance in the paint and varnish industries. 

 Examples include Hnseed oil, obtained from Flax, and its substitute 

 tung oil, obtained from two Chinese trees ; soybean oil, which is 

 widely used in human foods as well as industry, etc. ; and such 

 oils as perilla, walnut, Niger seed, hempseed, poppy, and safflower. 



2. Semi-drying oils, which form a soft film only after long exposure, 

 examples being cottonseed oil, obtained from Cotton, and used for 

 human food, animal fodder, fuel, and in a variety of industries ; 

 sunflower oil, obtained from the common Sunflower, used for the 

 same purposes as cottonseed oil and also in the paint, varnish, and 

 soap industries ; and such oils as corn, rape, and camelina. 



3. Non-drying oils, which remain liquid at ordinary temperatures. 

 These include olive oil, obtained from the Olive and used principally 

 for food and in medicine (though inferior grades are employed in 

 soap-making and as lubricants) ; its widely-used substitute, peanut 



