October ig, 191 1] 



NATURE 



535 



diseases of plants. Prof. Potter opened with a summary 

 of our present knowledge of the subject. The old idea that 

 the plant was not susceptible to the attacks of bacteria 

 is now known to be erroneous ; indeed, certain bacterial 

 diseases can be faithfully reproduced with absolute 

 certainty by inoculation in healthy tissues. The plant 

 possesses many vulnerable points of attack ; infection may 

 take place through the water pores, the stomata, the 

 floral nectaries, and wounds, the vessels of the xylem 

 affording a suitable channel for the dispersion of the 

 invading bacilli. Further, certain bacteria secrete a toxin 

 and cytolitic enzyme which destroy the protoplasm and 

 rapidly dissolve cellulose. The actual penetration of the 

 bacterium through the cell-wall has been observed. A 

 complete homology has been established between the 

 parasitism of bacteria and that of various fungi. Sapro- 

 phytic bacteria, like fungi, develop under certain conditions 

 into virulent parasites, and their aptitude as parasites may 

 be increased or suppressed by variations in nutrition. The 

 nature of the soil, manurial treatment, and other factors 

 materially affect the constitution of the host and its pre- 

 disposition to infection. Mr. Brooks followed with an 

 account of the gum disease of the sugar-cane, caused, as 

 Irwin F. Smith has shown, by a specific bacterium, 

 Pseudomonas vascularum. A disease of cherry trees, 

 accompanied by profuse gumming, has been traced by 

 Aderhold and Ruhland to Bacillus spongiosus. On the 

 other hand, the mosaic disease of the tobacco plant, 

 formerly attributed to bacteria, is now regarded as the 

 result of some physiological disturbance within the plant. 



Dr. Pethybridge described his investigations on the 

 bacterial diseases of the potato plant in the west of 

 Ireland. From a confused group of diseases formerly 

 known as " yellow blight " he has disentangled a definite 

 disease, "black stalk rot," resembling the "black leg" 

 of other authors, and caused by an organism which he 

 names Bacillus melanogenes. The organism not only 

 brings about the untimely death of plants in the fields, 

 but also causes a most serious rot in stored potatoes, even 

 healthy unwounded tubers being capable of infection 

 through their lenticels. 



Mr. A. S. Home emphasised the effect of external con- 

 ditions on the incidence of disease. The probability that a 

 plant will thrive in a given spot depends upon certain 

 combinations of factors relating, respectively, to (i) the 

 structure and internal constitution of the plant and the 

 organisms associated with it; (2) the soil and soil 

 organisms; (3) the climate, season, and aerially-borne 

 organisms. Disease may occur if the optimum arrange- 

 ments of the factors be disturbed. 



Another day was spent in considering how best the 

 university agricultural departments can come into contact 

 with the practical farmer. Mr. R. Hart-Synnot opened 

 with a description of the Irish system and a modification 

 that seemed suitable to English conditions. It is admitted 

 that the English system has not been entirely successful ; 

 indeed, it became evident in the discussion that some of 

 the most successful departments have broken altogether 

 from the conventional lines. Principal Ainsworth Davies 

 considered that the universities should not only undertake 

 research work and the training of experts, but should also 

 disseminate the results obtained among the farmers, and 

 act as bureaus of information generally. Mr. Burton dealt 

 with the place of the agricultural instructor, whose title. 

 he thought, ought to be changed to that of agricultural 

 adviser. 



A group of papers came in from the Cambridge Agri- 

 cultural Department. Prof. Wood and Mr. Harvey 

 described a very ingenious method of determining the 

 baking strength of single ears of wheat. Hitherto it has 

 been necessary to work with large quantities of flour, 

 which can only be obtained with difficulty in plant-breed- 

 ing experiments. The method suggested simply requires 

 one gram of flour. On shaking with water an opalescent 

 extract is obtained, the humidity of which affords a 

 measure of the strength of the wheat. The sensitiveness 

 of the method is increased by addition of iodine to the 

 turbid extract. Mr. H. A. D. Neville gave a preliminarv 

 description of the mucilage of linseed. On hydrolysis with 

 sulphuric acid, mucilage yields dextrose, galactose, 

 arabinose, xvlose. and small amounts of a cellulose-like 



NO. 2I90, VOL. 87] 



substance and of an acid which forms a soluble barium 

 salt. It appears to be completely digested by the animal, 

 but is neither acted upon by saliva nor by pancreatic 

 juice ; it is rapidly decomposed, however, by the bacteria 

 of the cascum. Messrs. Marshall and Mackenzie intro- 

 duced a technical subject of very great importance — the 

 question of ovariotomy in pigs. This practice has been 

 known for many years, but has not hitherto received the 

 scientific attention it deserves. If the ovaries are removed 

 after sexual maturity is reached, the uterus undergoes a 

 gradual atrophy ; on the other hand, the removal of the 

 uterus has no effect on the development or functional 

 activity of the ovaries. Further, if the ovaries are only 

 incompletely removed, a fragment left behind may in the 

 course of a few months regenerate into an ovary of con- 

 siderable size. Ovariotomy frequently results in a deposi- 

 tion of fat in various parts of the body ; hence its com- 

 mercial value. In a second paper the same authors dealt 

 with the temperature variations during the cestrous cycle 

 in cows. The rise may be as much as 5°, whilst on the 

 approach of heat a rise of 2° or 3 was usual. These 

 results have special importance in connection with the 

 tuberculin test, in which an animal is supposed to react 

 if the temperature rises 2°. 



Mr. H. W. Elwes gave an account of aboriginal races 

 and little-known breeds of domestic sheep, which elicited 

 an interesting discussion, in which Profs. Ridgeway and 

 Wilson, the chairman, and others took part. Domesticated 

 animals seem to have been curiously neglected by zoo- 

 logists, and Mr. Elwes could find only few references to 

 them in zoological literature. By dint of much inquiry 

 in remote and comparatively inaccessible regions of the 

 British Islands and elsewhere, he has succeeded in finding 

 a number of aboriginal breeds interesting not only in their 

 relationship to our present breeds, but because of their 

 potential value to the practical man, inasmuch as they are 

 extremely hardy and might be used to restore to some of 

 our present breeds the constitution that has been partially 

 lost. Another livestock subject was dealt with by Mr. J. 

 Hendrick in his discussion of the effects of ventilation on 

 the temperature and carbon dioxide content of the air of 

 byres. The amount of pollution is sometimes extra- 

 ordinary, more than 100 parts of carbonic acid per 10,000 

 having been recorded, whilst the average CO, content was 

 30 parts where ventilation was restricted and 12 to 15 

 where it was freer. In spite of the low temperature 

 resulting from free ventilation, the health of the cows was 

 better and their yield of milk was as good as in the warm, 

 badly ventilated byres. 



Messrs. Barker and Hillier described a disease known 

 as cider sickness that causes a loss probably amounting 

 to several thousand pounds sterling each year in the west 

 of England alone. It is brought about by a bacterium 

 capable of fermenting dextrose and laevulose with produc- 

 tion of alcohol and carbon dioxide, together with a small 

 amount of hydrogen, an unrecognised acid, and an odour 

 resembling that of decaying lemons. It does not appear 

 to attack saccharose, maltose, or lactose. Prof. Priestley 

 and Miss Lee described an ingenious method of measuring 

 the effects of various factors on the growth of micro- 

 organisms. The rate of production of the metabolic pro- 

 ducts as measured by the change in electrical conductivity 

 of the culture solution is taken as an index of growth, 

 and is found to give results in accordance with the much 

 more tedious process of counting. The particular factor 

 investigated was the influence of electricity. Currents up to 

 about 60 micro-amperes had a favourable effect on the rate 

 of growth of Bacillus bulgaricus, whilst currents of greater 

 strength inhibited their activity. No difference could be 

 detected between the effects of direct and alternating 

 currents. In a paper with Mr. Knight, Prof. Priestley 

 dealt with the influence of electricity on the respiration of 

 germinating seeds ; a direct current was found to be 

 harmful ; a rapidly alternating current at low strength 

 stimulated respiration, but had no effect at 150 micro- 

 amperes ; whilst stronger currents caused a decrease ; the 

 overhead discharge gave irregular results until some 

 turpentine was introduced to absorb the ozone produced, 

 and then an increase was observed in the amount of 

 carbonic acid produced. 



After a suggestion for the reform of the British system 



