CELLS AND CELL PRODUCTS 223 



not above 40 C. for fear of changing the character of the contained sub- 

 stances, and they should then be finely powdered. When only a small 

 quantity of material is available, it has been recommended that reagents 

 should be applied and the effect watched under the microscope with a low 

 power magnification. This method is also of great service in determining 

 the exact position of the acids in the thallus. 



In microchemical examination, Senft 1 deprecates the use of chloroform, 

 ether, etc., seeing that their too rapid evaporation leaves either an amorphous 

 or crystalline mass of material which does not lend itself to further examina- 

 tion. He recommends as more serviceable some oil solution, preferably 

 "bone oil" (neat's-foot oil), in which a section of the thallus should be broken 

 up under a cover-glass and subjected to a process of slow heating; some 

 days must elapse before the extraction is complete. The surplus oil is then 

 to be drained off, the section further bruised and the substance examined. 



Acids in bulk should be extracted by ether, acetone, chloroform, 

 benzole, petrol-ether and lignoin or by carbon bisulphide. Such solvents as 

 alcohols, acetates and alkali solutions should not be used as they tend to 

 split up or to alter the constitution of the acids. For the same reason, the 

 use of chloroform is to a certain extent undesirable as it contains a percentage 

 of alcohol. Ether and acetone, or a mixture of both, are the most efficient 

 solvents, and all acids can be extracted by their use, if the material is left 

 to soak a sufficient length of time, either in the cold or warmed. It is 

 however advisable to follow with a second solvent in case any other acid 

 should be present in the tissues. Concentrated sulphuric acid dissolves out 

 all acids but often induces colour changes in the process. 



All known lichen-acids form crystals, though the crystalline form may 

 alter with the solution used. After filtering and distilling, the residue will 

 be found to contain a mixture of these crystals along with other substances, 

 which may be removed by washing, etc. 



c. CHARACTER OF ACIDS. Many lichen-acids are more or less bitter to 

 the taste; they are usually of an acid nature though certain of the substances 

 are neutral, such as zeorin, a constituent of various Lecanoraceae,Physciaceae 

 and Cladoniaceae, stictaurin, originally obtained from Sticta aurata, lei- 

 phemirk from Haematomma coccineum, and others. 



A large proportion are esters or alkyl salts formed by the union of an 

 alcohol and an acid; these are insoluble in alkaline carbonates. It is con- 

 sidered probable that the fungus generates the acid, while the alcohol arises 

 in the metabolic processes in the alga. It has indeed been proved that the 

 alcohol, erythrit, is formed in at least two algae, Protococcus vulgaris and 

 Trentepohlia jolithns ; and the lichen-acid, erythrin (C^ H^ O 10 ), obtained 

 from species of Roccella in which the alga is Trentepohlia, is, according to 



1 Senft 1907. 



