246 THE ARTIFICIAL CULTIVATION OF DIATOMS. 



needed in the culture of microbes, already isolated in a state of 

 purity. 



Six months of almost daily labour will be required to secure a 

 natural stock of one diatom, even of a common species, i7i a state 

 of absolute ptirity. I would not, therefore, advise observers to 

 commit themselves to researches, which happily are not indispens- 

 able to the study of the morphology of the Diatoms. The culti- 

 vation of species in a state of purity, freed from infusoria, green 

 algae, and fungi, are certainly sufficient. In the meantime, if you 

 wish to study the phenomena of the nutrition of the diatoms, 

 learn what are the aliments that they absorb, the products that they 

 secrete, the changes that they introduce in the mixtures charged 

 with mineral salts and organic matters, the separation of the 

 frustules in a state of absolute parity, is absolutely called for. It 

 is on this account that I have believed I ought briefly to indicate 

 the process — long, it is true, but more complicated in appearance 

 than in reality, which admits of success in this direction. 



I do not despair, in the long run, of simplifying this latter 

 method. We shall assuredly come to it when we know better the 

 half-solid mediums which in an especial manner favour the develop- 

 ment of the interesting algse that have claimed our attention. 



Test for Sesame Oil. — G. Ambiihl states that, though the green 

 colouration of this oil when mixed with nitric and sulphuric acids 

 allows the pure oil to be distinguished from olive, cotton-seed, or 

 earth-nut oil, the detection of an admixture of sesame oil is best 

 effected by shaking the suspected oil with sugar and hydrochloric 

 acid. When sesame oil is present, the watery liquid immediately 

 becomes intensely red. The other oils do not give this reaction, 

 except in the case of the oil from Bari, and that differs from oil 

 mixed with sesame oil in giving the red colouration only after some 

 length of time. — Schweitz. Wochensch. Pharm. 



