346 



SCIENTIFIC NEAVS. 



[April 13, 1888. 



plugged and constricted extremity. That end is then 

 attached by means of a piece of stout india-rubber 

 tubing to a piece of lead tubing about 10 feet in length, 

 which is clamped at this end to a retort stand, whilst the 

 other extremity of the lead tube is attached to an ex- 

 hausting syringe, which is mounted on a rigid support 

 placed upon the ground. By bending the lead tubing 

 the glass experimental tube is brought into a horizontal 

 position, and in out-of-door experiments the open ex- 

 tremity is turned away at an angle of 45" from the 

 direction of the wind. An ordinary mercury pressure 

 gauge is also attached to the lead tubing, and properly 

 supported on the ground. A mirror is placed obliquely 

 on the ground to enable the operator to watch the rise 

 and fall of the mercury in this pressure gauge. 



After each upward stroke of the pump, the experi- 

 mentalist waits until the pressure is equalised before 

 making the down stroke. In this way each stroke of the 

 pump corresponds to the passage through the experi- 

 mental tube of a definite quantity of air. The number 

 of strokes measures the volume of air aspirated, and the 

 number of strokes per minute indicates the degree of 

 perviousness which the plugs possess. In Dr. Frank- 

 land's apparatus, one stroke of the air-pump was 

 equivalent to i8 cubic inches. The volume of air 

 aspirated was varied according to the number of 

 micro-organisms supposed to be present, but with ordinary 

 London air 60 strokes of the pump were found to be 

 convenient. 



Dr. Frankland employed the system of flask cultivation 

 for the treatment of the experimental plugs. These 

 were of carafe shape, and of 20 to 25 cubic inches 

 capacity, containing about | cubic inch of gelatine- 

 peptone, all being properly sterilised and having cotton- 

 wool stoppers. The gelatine in these flasks has been 

 melted at a temperature of 86'=' Fahr. The tube through 

 which air to be tested has been aspirated is withdrawn 

 from the sterile box, care being taken to handle it by the 

 plugged extremity. A scratch is made with a file about 

 the middle of the tube, and the tube carefully broken 

 across. The half containing the two plugs is carefully 

 laid aside on a sterile support ; but the other half with 

 the experimental plug is held between the thumb and 

 first finger at the constricted part, and the broken edge 

 passed two or three times through a Bunsen flame, care 

 being taken that the heat does not reach the plug. The 

 cotton-wool stopper of one of the gelatine flasks is then 

 withdi-awn, and the open extremity of the tube is held 

 vertically over the open flask, whilst the plug is carefufly 

 pushed down by means of a strong piece of sterilised 

 copper wire, introduced from behind through the broken 

 part of the tube. 



The plug having been thus forced into the flask, the 

 cotton-wool stopper is replaced. A similar process is 

 gone through with the second plug. The gelatine in 

 each flask is then agitated with the plug by means of a 

 rotatory movement. In a few minutes the plug is quite 

 broken up. The flask is now held almost horizontally 

 under a stream of water, and by uniformly rotating it 

 an almost perfectly even film of gelatine is spread over 

 its inner surface. The stream of water must be 

 sufficiently cold to prevent the gelatine from forming 

 lumps. 



The flasks, thus coated internally with the film of 

 gelatine and germs, are allowed to remain for an hour or 

 so in a cool place. They are then placed under a bell- 

 jar, the internal air of which is kept saturated with 



moisture by means of blotting-paper soaked in water. 

 The contents of the flasks are allowed to incubate at a 

 temperature of about 70° Fahr. for a period of four or 

 five days. The counting of the colonies after incubation 

 is effected with great ease by dividing the flasks with ink 

 into segments, and holding them up against the 

 light. 



Dr. Frankland has found that the organisms are 

 almost invariably arrested by the first plug, the second 

 plug only occasionally yielding any, though it was far 

 more impervious than the first. It seems, therefore, that 

 experiments can be quite successfully made with a 

 one-plug apparatus, which will save much time and 

 expense. He found, among hundreds of recorded 

 experiments, that at St. Paul's Cathedral there were 

 30 colonies of micro-organisms in a cubic foot of air 

 from the Golden Gallery, 120 colonies per cubic foot of 

 air from the Stone Gallery, and 140 from the air of the 

 churchyard. 



Dr. Frankland considers his new method to have 

 several advantages over Hesse's best process. It pos- 

 sesses all the well-recognised advantages pertaining to the 

 use of a solid cultivating medium. The results can lay 

 claim to a higher degree of quantitative accuracy. The 

 results are not appreciably affected by aerial currents, 

 which prove such a disturbing factor in the results 

 obtained by some other methods. The collection of an 

 adequate sample of air occupies a much shorter space of 

 time. Thus, whilst the aspiration of a cubic foot of air 

 through Hesse's apparatus takes about 2| hours, by 

 the new method it only takes about half-an-hour. As the 

 whole plug upon which the organisms from a given 

 volume of air are deposited is submitted to cultivation 

 without subdivision, no error is introduced through the 

 multiplication of results obtained from aliquot parts. 

 The risk of aerial contamination in the process of flask- 

 cultivation is practically nothing. The apparatus being 

 very simple and easily carried, the method is admirably 

 adapted for the performance of experiments at a distance 

 from the laboratory. 



The deep interest which the general as well as the 

 scientific public is taking in the subject of micro- 

 organisms in the air is a sufficient excuse for the 

 detailed explanations of the several methods of quanti- 

 tative enumeration which we have abridged from Dr. 

 Frankland's excellent communication. 



o^w^^Stf-* 



Cutlass Tests. — In order to more completely insure 

 the good quality of the cutlasses issued to the Navy, 

 orders have recently been given for the following tests to 

 be applied to a large number of the weapons, which are to 

 be repointed and reduced to a uniform blade length of 

 twenty-seven inches. First the cutlass is to be subjected 

 to a direct vertical pressure on the hilt in a machine 

 specially constructed for the purpose, and it is required 

 to stand a pressure of 40 lb. without deviating from the 

 straight line. Then additional vertical pressure is to be 

 applied in the machine until the cutlass is bent, so that 

 the distance from point to hilt is reduced three inches. 

 Finally, the blade has to be bent round a suitable curved 

 block, so that every portion of it partakes of the bend, 

 the distance from point to hilt being reduced two and 

 a half inches. The cutlass also has to be struck with 

 moderate force, back and edge, on a block of oak, to test 

 the soundness of the hilt. 



