In addition to these factors certain others are found to operate in reducing the rat catch, as, for example, weather conditions and the occurrence of Sundays, holidays and the days just preceding and following holidays.
Upon rainy days and the days just mentioned the rat catch almost invariably falls off.
From statistics collected by me in connection with this work, Dr. V. G. Heiser, then Director of Health for the Philippine Islands, published the following memorandum in 1914. As it is a correct transcript of my records I introduce it here in its entirety.
Comparative Statistics in Rat-catching Methods.[3]—With a view to ascertaining which type of rat trap was most effective and also the average number of rats that are caught by a given number of poisoned baits that are set out, statistics were kept during the antirat campaign in Manila. The ratio maintained in catching rats with two types of traps is indicated in the following [table], a perusal of which will show that for the three months ended June 30, 1913, there were 120,565 spring or snap traps set and that for every 100 of this type of trap set there were caught 6.9 rats. During the same period there were 47,075 wire cage traps set; the total number of rats caught was 339; which gives 0.72 rat caught for each hundred traps set. For the quarter ended September 30, 130,627 spring or snap traps were set and 9,753 rats were caught, which gives 7.47 for each 100 traps set. During this period 40,621 wire cage traps were set and 395 rats were caught, which gives 0.97 rat caught for each 100 wire cage traps set.
[3] Reprint from the Public Health Reports, Vol. 29, No. 6, February 6, 1914.
| [Kind of trap or poison] | Quarter ended June 30 | Quarter ended Sept. 30 | ||||
|---|---|---|---|---|---|---|
| Number set | Number of rats caught or poisoned | Per cent. | Number set | Number of rats caught or poisoned | Per cent. | |
| Spring or snap traps | 120,565 | 8,377 | 6.9 | 130,627 | 7,753 | 7.47 |
| Wire cage traps | 47,075 | 339 | .72 | 40,621 | 395 | .97 |
| Poison bacon, rice, or coconuts | 166,237 | 1,216 | .731 | 177,309 | 216 | .12 |
| Quarter ended— | ||||||
| June 30 | Sept. 30 | |||||
| Number of rats: | ||||||
| Caught by dogs | 160 | 5 | ||||
| Killed with clubs and other weapons | 2,889 | 3,818 | ||||
| Found dead from other causes | 316 | 297 | ||||
No accurate record was kept of the number of each kind of rat bait set. Only the total of all was recorded. Bacon or coconut with strychnine and rice with arsenic were used. For instance, for the quarter ended June 30, 1913, there were 166,237 poison baits set in new territory and the rats found poisoned average for each 100 baits 0.72. During the next quarter there were 177,309 baits set in territory that had been worked over, and only 216 rats, or 0.12 rat per 100 baits, were killed. From the foregoing it appears that the rat poison ranks lowest in efficiency but perhaps highest in economy. In view of the fact that the original cost of the cage trap is many times more than that of the spring trap, and the cost of maintenance is very high, it will be apparent that the spring trap is by far the more economical as well as more effective of the two.
Generally speaking, however, the number of rat catchers engaged and the location of their operations has the largest influence upon the total catch of rats. For the fiscal year July 1, 1912, to June 30, 1913, inclusive, the total catch was 55,101 rats (Manila only); to December 1, 1913, 79,676.
The most natural explanation of the general correspondence between the highest rat catch and the highest incidence of human plague would be upon grounds of greater activity in rat catching effort at times of greatest plague prevalence, but from the inauguration of general systematic rat catching there was no cessation of effort, even during the abatement of plague, and in consequence this explanation does not apply strictly.
It is true, however, that whenever plague occurred in districts theretofore free from the disease, rat catching was pushed vigorously in the surrounding localities.