CONTRIBUTIONS FROM THE WIS LEY LABORATORY. 



45 



small rectangular slices of tissue from 2 to 4 mm. thick. The 

 slices were either placed in the reagent directly after they had been pre- 

 pared, or they were first rinsed in water. According to Mandelin and 

 WoTHTSCHALL, in the presence of solanin the following colours appear 

 in order : yellow, orange, purple-red, brownish-red, carmine, rasp- 

 berry-red, violet, blue-violet, pale greenish blue; finally all colour dis- 

 appears. Series of non-etherized slices were used first. A series was 

 cut from a diseased area in an early stage of development, so that the 

 slices were only slightly discoloured. A second series was then taken 

 from a similarly situated non-diseased area of the same potato. The 

 two series were simultaneously immersed in the reagent, wh^ch was 

 contained in white porcelain dishes standing side by side. Every test 

 performed in this way showed a stronger colour reaction in the 

 diseased than in the non-diseased tissue. A test was then made, using 

 similarly situated slices from potatos of two different varieties — in this 

 case the ' Factor ' and * Northern Star. ' There was no appreciable 

 difference in the reaction. Since G. Meyer''' and von KlepzowI in a 

 quantitative test record slightly more solanin in the sub-cuticular tissue 

 than in the starch-parenchyma of potatos, some slices were taken from 

 the pith and the sub-cuticular parenchyma of a tuber of * Factor ' to 

 see whether a difference could be detected by the qualitative method. 

 In this case the section from the pith showed a slightly less strong 

 reaction. 



. If fatty oils were present in the tissue, these might give colour 

 reactions with sulphuric acid and interfere with the test. Solanin is 

 stated to be practically insoluble in ether. If this be the case the slices 

 may be extracted with ether and so eliminate this chance of error 

 before applying Mandelin 's reagent. Accordingly a number of slices 

 were prepared and soaked in ether for 48 hours. The experiment was 

 first made of transferring the slices from the ether to blotting-paper and 

 thence to the reagent. In a second experiment, the parallel series of 

 slices were transferred from the ether to the reagent simultaneously. 

 In both cases the colour reaction was stronger in the diseased tissue 

 and the sections in every case passed through the scale of colours in 

 the proper order. 



There are several difficulties and possible sources of error in per- 

 forming this test. If the slices be placed in a small quantity of the 

 reagent, the liquid needs to be frequently changed, and since the reaction 

 takes several hours, the slices may be rendered useless before they 

 have passed through the complete series of colour changes. Almost 

 immediately after immersion in the reagent the slices become opaque 

 owing to the presence of innumerable minute bubbles, which interfere 

 with the colour effect. The same error, however, occurs in both 

 series. The intensity of colour shown by a particular slice is influenced 

 by the number of vascular bundles which it contains. These take an 

 intense colour, many times more intense than that shown by the starch 



* G. Meyer. Archiv txp. Pathol. , Bd. xxvi. (1895), p. 361. 

 t Klepzow. Just Jahresb. 1895, Bd. ii. (1890), p. 245. 



