Nov. 3,1923 Five Molds and their Penetration into Wood 
221 
conditions. Slivers of wood from the interior of the test blocks, the 
surfaces of which had been washed off with a solution of mercuric chlorid, 
were introduced into tubes of malt agar. These transfers indicated, after 
growing for a time, that each of the five original molds was alive and pure 
well below the surface of the block. 
The eleven cultures, which had been set aside for further growth, when 
inspected on August 23, 1921, were apparently uncontaminated and 
still growing. They were not reinspected until September 19, 1921, at 
which time it was found that, after growing without apparent contami¬ 
nation for two years, the entire set had suddenly become seriously con¬ 
taminated. It was concluded that there had probably been an infesta¬ 
tion with mites. It was felt, however, that since the contaminating 
growth was of comparatively recent origin, information of some value 
might be obtained by examining this material, although the results 
could only be considered as supplementary and indicative, rather than 
conclusive. The examinations were made and yielded evidence in agree¬ 
ment with that obtained from the thorough study of the five pure cul¬ 
tures of the first series, which finally were the source of all the pure 
culture material available for study as a result of this test. 
METHODS OF EXAMINATION 
• Microtome sections were cut from the test blocks which had been pre¬ 
served in formalin and alcohol and later soaked in glycerin and alcohol. 
Care was taken to obtain areas from the interior, as well as from the sur¬ 
face, of the block in order that the character of the penetration of the 
different organisms might be thoroughly examined. Some cross sec¬ 
tions were cut, usually midway between the ends of the block. The 
longitudinal sections both radial and tangential were, however, on the 
whole, more satisfactory for study. 
METHODS OF STAINING 
The hyphae of these molds were for the most part colorless; often they 
were very fine. Therefore, in order to facilitate the examination and 
the determination of the extent and character of the penetration of the 
molds by differentiating more clearly the mycelium from the host tissue, 
some experiments were made with stains. A number of stains used for 
this purpose have been described 3 (5, 6, 8 , 18 , 19 , 20 ); these were tried 
by the writer but did not appear entirely satisfactory. One very help¬ 
ful staining method has been published since these tests were made ( 11 ). 
It was felt that since fungi are understood to contain a very distinctive 
membrane substance (chitin), some selective reaction could be found to 
bring out a contrast between the membranes of the fungous hyphae and 
of the wood. At the suggestion of Dr. M. E. Diemer, experiments were 
made with the application of gold and silver solutions. A preliminary 
note on the use of these solutions has been published (9). Some of the 
results obtainable are illustrated in Plates 2, 3 , and 4. 
The methods employed with various reagents and the results obtained 
are given below in detail. The staining considerably facilitated the ob¬ 
servations on the extent of the penetration of the molds in the case in 
hand, although insufficient time was spent to perfect, in a comprehensive 
manner, the technique of applying the methods developed. The stains 
used were found to give good results in photomicrographing the material. 
* Reference is made by number (italic) to ** Literature cited,” p. 228-229. 
